Semi-conductor to provide a step current function with plural emitters which inject minority carriers



Dec. 3, 1963 J. R. CZACZKOWSKI 3,113,222

SEMI-CONDUCTOR TO PROVIDE A STEP CURRENT FUNCTION WITH PLURAL EMITTERS wHIcH INJECT MINORITY CARRIERS Filed July 51, 1961 an; "1"; n

//M/ 5/ /M3 53 45 '/E5 /%M 2 El E4 M4 E3 H62 r l i E i 5 M5 I 1 1 l lNvENToR United States Patent dEMl-CONDUCIOR TO PROVIDE A STEP CUR- RENT FUNEIION WlTH PLURAL EMITTEIRS WHICH INEECI MINORITY CARRIERS .lerzy Roman Czaczkowslsi, Harrow, England, assignor, by mesne assignments, to North American Philips Company, Inc, New York, N.Y., a corporation of Delaware Filed July 31, N61, Ser. No. 128,059 Claims priority, application Great Britain Aug. 2, 1960 Claims. (Cl. 307-885) This invention relates to semi-conductor devices and has for its object to provide improved semi-conductor devices which will provide any of a number of different values of current flow in response to different values of applied potential, the current value increasing in steps, i.e. sharp increments, if the applied voltage is increased progressively. In other words the invention seeks to provide a semi-conductor which will produce what may be termed a staircase function of current from a linearly or progressively increasing applied voltage.

According to this invention a semi-conductor device comprises a base member with main electrodes on both sides thereof so arranged that each main electrode on one side has portions opposite portions of two adjacent spaced electrodes on the other side and a portion opposite a space between said two adjacent spaced electrodes so as to provide a path extending back and forth through said base member from one electrode to an electrode on the opposite side of said base member, then to another electrode on the first side of the said base member and so on; means for injecting minority carriers in the diiferent parts of said base member between electrode portions on either side thereof; and means for applying potential to an electrode at one end of said path whereby, if the applied potential is increased, so-called punch through occurs successively, for different values of the increasing applied potential, through the aforesaid different parts of said base member.

Preferably the means for injecting minority carriers comprise emitter electrodes on opposite sides of said base member, each spaced from and adjacent one of the main electrodes, and means for applying predetermined potentials to said emitter electrodes. It is, however, possible to arrange for the injection of minority carriers in other ways, e.g. by activation with light or other forms of energy capable of producing minority carriers in a semiconductor.

In one way of carrying out the invention the applied potential is applied between a main electrode at one end of the path and a specially provided electrode adjacent the other end of said path. Alternatively the applied potential may be applied between a main electrode at one end of the path and a specially provided electrode spaced from all the main electrodes on the same side of the base member. In a preferred arrangement as last described, the said main electrodes on the same side of the base member are spaced apart along an arc with the specially provided electrode centrally arranged with respect thereto.

The emitter electrodes, where provided, may conveniently be located each approximately centrally in the space between two adjacent main electrodes on the same side of the base member, but obviously this is not a necessary arrangement and other locations for the emitter electrodes are possible.

The invention is illustrated in the accompanying simplified schematic drawings in which FIGS. 1 and 2 are respectively a sectional view and a plan view of one embodiment; FIG. 3 is a plan View illustrating a minor modification of the embodiment of FIGS. 1 and 2; FIG. 4 is a plan view of a further modification. In

describing the drawings it will be assumed that the devices in question are of the p-n-p type. Obviously, however, the invention can be equally well embodied in devices of the n-p-n type in which case, of course, the base member would be a p-type semi-conductor instead of an n-type semi-conductor.

Referring to FIGURES l and 2 the device therein shown comprises a lamina 1 of high resistivity n-type semi-conductor material. This lamina constitutes the base member of the device. On one side of the lamina is a series of spaced p-type main electrodes M1, M3 and M5. Although only three such electrodes are shown there may be any desired number. Centrally positioned in the inter-electrode spaces MI-M3 and M3-M5 and to the far side of the electrode M5 are three emitter electrodes E1, E3 and E5. Beyond the electrode E5 is a final electrode F shown in FIGURE 1 in heavy black lining and in FIGURE 2 by cross hachuring. The electrodes M1, M3 and M5 and El, E3 and E5 also appear in FIGURE 2 where they are shown by hachured areas. On the other side of the lamina 1 are three further spaced p-type main electrodes M2, M4 and M6 with emitter electrodes E2, E4 between them as shown in FIGURE 1. As shown in FIGURE 1, the electrode M2 is symmetrical with respect to and overlaps the electrodes M1 and M3 and has a central portion opposite the space MIM3 and therefore opposite the electrode E1 and end portions opposite the adjacent ends of the electrodes M1 and M3. Electrodes M4 and M6 are correspondingly positioned, M4 overlapping the electrodes M3 and M5, and M6 overlapping the electrode M5. Potential is applied at terminals T1 and T2 between M1 and F, T1 being shown as negative with respect to T2 which is taken as Zero or datum potential. The remaining main electrodes M2, M3, M4, M5, and M6 float, no voltage being applied. A suitable positive potential is applied from terminal T3 through the resistances shown to the emitter electrodes E1-E5 which accordingly inject minority carriers in the base member so that a number of holes Will be injected opposite each of the main electrodes, these holes being collected by the opposite main electrodes which will consequently charge positively, the latter being closer to the opposed emitter than the adjacent main electrodes. So as not to complicate the figure, the connections are not shown in FIGURE 2. For simplicity in FIGURE 1 the emitter electrodes are shown as all connected to the same terminal, but if desired independent or independently adjustable potentials may be applied to the individual emitter electrodes.

The arrangement operates as follows: Suppose the potential between terminals T1 and T2 to be rising. At first the current through the back-biased electrode M1 will rise until it reaches the saturation value corresponding to the size of the junction and the prevailing surface condition in its vicinity. On further rise of potential the increase of current will be insignificant until the voltage reaches the punch through value from M1 to M2, i.e., when the depletion layer extending from M1 reaches M2 producing an effective short-circuit between them. When this value is reached practically all the holes injected by the junction El-base member and collected by the electrode M2 will be contributing to the total current through M1 and a sudden increase of current will occur. This increased value of current will be maintained substantially unchanged as the applied voltage increases further until the voltage reaches a new value at which punch through from M2 to the electrode M3 occurs when there will again be a sudden rise in the current by an amount dependent on the number of holes injected by the emitter E2. A similar sequence of events occurs as the applied voltage rises still further,

punch through taking place from M3 to M4 and then from M4 to M and so on. In this way a continually rising applied voltage will produce a staircase function of current, the current rising in sudden steps each occurring at a different punch throng The invention is not limited to the particular arrangement shown in FIGURES 1 and 2. As regards dimensions, it should be noted that FIGURES 1 and 2 are schematic and not intended to be to scale. It should be remarked, however, that the spacing a between the edge of a main electrode and the adjacent edge of the nearest emitter electrode should be significantly greater than the thickness spacing b in the base member between the inner faces of overlapping portions of main electrodes on opposite sides of the base member. For clarity of drawing, the thickness b is shown as a good deal greater relative to dimension a than it would be in practice.

It is not necessary that the emitters be centrally positioned in relation to their respective collectors or main electrodes and FIGURE 3 shows, so far as is necessary to an understanding thereof, part of a modification in which the emitters are at the sides of the collectors. In FIGURE 3, which is shown broken away, main electrodes Ml, M3 and M5 on one side of the base member I are represented by the full line rectangles and the overlapping main electrodes M2 and M4 on the other side of the base member are represented by the broken line rectangles. Similarly the emitter electrodes E1, E3 on one side of the base member are shown in full lines and emitter electrodes E2 and E4 on the other side are shown in broken lines. In other respects the construction of FIGURE 3 is like that of FIGURES 1 and 2 and it operates in a similar manner.

In the further modification shown in FIGURE 4 the main electrodes are disposed in arcuate fashion on opposite sides of a disc-like base member, here referenced 11, as also are the emitter electrodes, main and emitter electrodes on one side of the base member being shown in full lines and those on the other side being shown in dotted lines. In FIGURE 4 the main and emitter electrodes on one side are referenced M1, M3, M5, M7, M9, El, E3, E5 and E7, while the electrodes on the other side are referenced M2, M4, M6, M8, E2, Ed and E6. Potential is applied between terminal T1 connected to electrode M1 and a centrally situated disc-like final electrode F to which terminal T2 is connected. Suitable potentials are applied to the emitter electrodes as before, through connections not shown.

By providing connections with successive main electrodes, on one side of the base member, a device in accordance with this invention may be operated as a voltage sensitive switch allowing currents to different circuits connected to those electrodes to be switched on in dependence on the value of the voltage applied between terminals T1 and T2.

As already stated individually controlled voltages may be applied to the individual emitter electrodes. Also it is possible to carry out the invention without using emitter electrodes at all, the necessary injection of holes being achieved in any other manner known per se, e.g. by suitably directed localised spots of light or other sources of energy able to produce minority carriers in a semi-conductor.

I claim:

1. A semiconductor :device comprising a semiconductor base member having opposed major surfaces, plural spaced main electrodes on both major surfaces of said base and arranged such that each intermediate main electrode is arranged opposite the space between adjacent electrodes at the opposite surface and including portions arranged opposite portions of said adjacent opposed electrodes, means for injecting minority carriers into the base member at each of the spaces between the said main electrodes,

.and means for applying an increasing potential to one of said main electrodes in the back direction and at which punch-through successively occurs between opposed electrodes in the body at increasingly higher values of the applied potential causing stepped increases in the current flow through said base member.

2. A semiconductor device comprising an elongated semiconductor base member of one type conductivity having opposed major surfaces, a first series of plural spaced regions of opposite type conductivity within said base member extending generally along a line adjacent one major surface of said base member and defining plural p-n junctions, a second series of plural spaced regions of opposite type conductivity within said base member extending enerally along a line parallel to said aforementioned line adjacent the opposite major surface of said base member and defining plural p-n junctions, a connection to the first region of said first series, an ohmic connection to said base member, each of the regions in the first and second series except for the first and last regions being arranged opposite the space between adjacent regions at the opposite major surface and including end portions that overlap end portions of said adjacent opposed regions, emitter electrodes for injecting minority carriers into the base member at each of the spaces between the said regions, said emitter electrodes each being spaced closer to the region at the opposite major surface than to the adjacent regions on the same major surface as the said emitter electrode, means for biasing the emitter electrodes in the forward direction whereby the injected carriers flow toward and are collected by the region on the opposite major surface, and means for applying a potential across said connections which biases the first region in the back direction, said remaining regions floating, said opposed regions being spaced apart distances at which, when an increasing potential is applied between the aforesaid connections causing the regions to become backbiased, punch-through successively occurs between opposed regions in the body commencing from the first region onward at increasingly higher values of the applied potential causing stepped increases in the current flow through said base member.

3. A device as set forth in claim 2 wherein the ohmic connection is on the same major surface of the base member as the said first region of said first series.

4. A device as set forth in claim 3 wherein the said line along which the regions extend is curved to form an arc, said ohmic connection being disposed generally at the center of the arc.

5. A semiconductor device comprising an elongated semiconductor base member of one type conductivity having opposed major surfaces, a first series of plural spaced regions of opposite type conductivity within said base member extending generally along a line adjacent one major surface of said body and defining plural p-n junctions, a second series of plural spaced regions of opposite type conductivity within said base member extending generally along a line parallel to said aforementioned line adjacent the opposite major surface of said base member and defining plural p-n junctions, a connection to the first region of said first series at one end of said base member, an ohmic connection spaced from the said regions to the opposite end of said base member, each of the regions in the first and second series except for the first and last regions being arranged opposite the space between adjacent regions at the opposite major surface and including end portions that overlap end portions of said adjacent opposed regions, emitter electrodes for injecting minority carriers into the base member disposed centrally at each of the spaces between the said regions, said emitter electrodes each being spaced closer to the region at the opposite major surface than to the adjacent regions on the same major surface as the said emitter electrode, means for biasing the emitter electrodes in the forward direction whereby the injected carriers flow toward and are collected by the region on the opposite major surface, and means for applying a potential across said conne tions which biases the first region in the back direction,

said remaining regions floating, said opposed regions being higher values of the applied pstential causing stepped spaced apart distances at Which, when an increasing poincreases in the current flow through said base member.

"fl a 4 M; a n Fennel is apgned bemoan the aforwnid cJrinccilone cans References Clted m the file of fins patent mg the regions to become back-biased, punch-through T successively occurs between onposed regions in the body URITED STATES PATENTS commencing from the first region onward at increasingly 2 801,347 Dnge July 30, 1957 

1. A SEMICONDUCTOR DEVICE COMPRISING A SEMICONDUCTOR BASE MEMBER HAVING OPPOSED MAJOR SURFACES, PLURAL SPACED MAIN ELECTRODES ON BOTH MAJOR SURFACES OF SAID BASE AND ARRANGED SUCH THAT EACH INTERMEDIATE MAIN ELECTRODE IS ARRANGED OPPOSITE THE SPACE BETWEEN ADJACENT ELECTRODES AT THE OPPOSITE SURFACE AND INCLUDING PORTIONS ARRANGED OPPOSITE PORTIONS OF SAID ADJACENT OPPOSED ELECTRODES, MEANS FOR INJECTING MINORITY CARRIERS INTO THE BASE MEMBER 